As shown in FIG. 4, an air bag assembly is disposed centrally on a vehicle steering wheel 10 so as to deploy and inflate an air bag when sensing impact or deformation upon collision of a vehicle. This air bag assembly includes a mounting plate, commonly referred to as a retainer. An inflator and an air bag are mounted to the mounting plate and covered by a modular cover 11. The modular cover 11 is fit over spokes 12 of the steering wheel.
The modular cover 11 has tear lines 13 along which the modular cover can be ruptured when the air bag is deployed. The tear lines are in the form of a continuous groove or a semicontinuous groove. The tear lines may alternatively include spaced grooves of greater depth. When the cover has two different layers, a rigid layer i.e. and a soft layer, a slit may be formed in the rigid layer so that the cover may be ruptured along a predetermined line.
As shown in FIG. 4, the tear lines 13 of the prior art modular cover 11 are formed on a top or main surface 11A and includes tear lines 13a,13b extending vertically along lateral sides of the main surface 11A, and another tear line 13c centrally and laterally of the cover 11. A vertical direction is a direction from an occupant M toward a windshield G, and a lateral direction is the width direction of a vehicle. In this case, the steering wheel is so oriented as to allow the vehicle to run on a straight line.
When such a conventional modular cover is molded, sinkmarks may be formed to cause wrinkles around the tear lines 13 on the top or main surface 11A of the modular cover 11. Those wrinkles, if quite visible, may deteriorate the esthetic appearance of the modular cover.
The occupant of a vehicle may rub such wrinkles with his fingers. This causes the tear lines to be repeatedly bent and deformed to reduce the durability of the modular cover 11.
A leather may overlie the main surface 11A of the modular cover to provide a high quality modular cover. In such a case, however, the leather may prevent the modular cover 11 from opening along the tear lines 13. As such, the leather can not be used in the prior art modular cover.